Purifying zinc



March 12, 1935. GINDER I 1,994,348

PURIFYING ZINC' Original Filed Dec. 20, 1932 3 Sheets-Sheet l ATTORNEYS March 12, 1935. P. M. GINDER 1,994,348

PURIFYING ZINC Original Filed Dec. 20, 1932 3 Sheets-Sheet 2 ATTORNEYS ,Wml

Mafch 12, 1935. GINDER I 1,994,348

PURIFYING ZINC Original Filed Dec. 20, 19-32 3 Sheets-Sheet 3 6 H Y O O 2W;

E vww fl momm Philip M. Ginder, ralmerton, 1a., assignor to To New Jersey Zinc Company, New York, N. 1., a. corporation of New Jersey Original application December 20, 1932, Serial No. 648,056. Divided and this application May 16, 1933, Serial No. 671,315

9 Cla (or. 75-28) This invention relates to purifying zinc gnetal by redistillation, and has for its object the, provision of an improved method of purifying zinc of lead and other metals of higher boiling points than zinc. The method of the invention is particularly adapted for purifying z'inc by the action of a reflux column as described in the copending application for Letters Patent of the United States of Leon 8.. Holstein and Philip M. Ginder, Serial No. 540,566, filed May 28, 1931. Throughout this specification and the appended claims, I have used the term reflux column to define a column or tower in which ascending metallic vapor moves in contact with descending (refluxing) molten metal resulting from condensation of ascending k vapor; a substantial amount of refluxing molten.

metal being permitted to flow out of the base of the column and metallic vapor reaching the top of the column being appropriately recovered,

The present invention aims to provide an improved method of purifying large amounts of zinc contaminated with lead or the like in a battery or system containing a number of separate distillation retorts, preferably operating in a substantially continuous manner. In. its broad aspect the invention involves distilling impure, zinc in a plurality of separate retorts operatively associated with individual reflux columns, and conducting the purified zinc vapor from each reflux column to a common condensing and collecting system. Preferably, the purified metal is collected in a relatively large accumulated reservoir maintainedin the molten state by supp n extraneous heat. thereto. The distillation system,

may be operated'in a substantially continuous manner by adding impure zinc metal of the grade to be purified to the retorts as required to maintain a substantially uniform volume of molten metal in each retort, and a refined zinc product of substantially uniform purity (with respect to lead) may be obtained by withdrawing lead-rich residues from the individual retorts at different times without interrupting the continuity of operation of the system and in such a way-that the total amount of lead present in theretorts remains substantially constant. These and other novel features of the invention will be better understood from the following description taken in conjunction with the accompanying drawings illustrating an apparatus particularly adapted for the practice of the invention. In the drawings,

Fig. 1 is a sectional end elevation of the apparatus,

Fig. 2 is a top plan, partly in section, of the pn Fig. 3 is a side elevation, partly in section of the apparatus, w

- Fig. 4 isa modified form of reflux column, and i .5 is an explanatory sectional elevation taken on the-section line 5-5 of Fig. 2.

The apparatusillustrated in Figs. 1, 2 and 3 of the drawings comprises'an elongated furnace structure 10 having a central longitudinal partitlon 11 dividing the interior of the furnace into two adjacent and. communicating heating chambers or laboratories 12. A horizontal row of zinc distillation retorts 13 is arranged in each heating chamber 12. The two horizontal rows of retorts are set back to back against the central wall 11 and are mounted at a slight inclination from the fear or backwoward the front where they extend through appropriate openings in the two side or front walls of the furnace structure. The

column comprises-a cylinder 15, of fire clay or other appropriate refractory material, having an opening in the bottom thereof registering and communicating with the upper end of the elbow 14. The top of the cylinder 15 is closed by a plate 16 appropriately luted with mud or the like to prevent the escape 'of zinc vapor. The cylinder 15 is surrounded by appropriate heat insulating material 17 (such as refuse zinc oxide) confined in place by a steel jacket 18 supported in its operative position in front of'the furnace in any appropriate manner. I

A'transverse perforated plate 19 is arranged within the cylinder 15 a short distanceabove the bottom thereof, and 'serves to support a column of sized filling material 20. The filling material may advantageously be coke crushed to about 4%;

inch, orany other-inertpacklng material such as crushed refractory, fire-clay brick etc.

One end of an elbow pipe 21' communicates with the top of the cylinder 15 approximate or slightlyabove the upperlevel of the filling material 20 therein. The other end of the elbow pipe 21 communicates with a downcomer 22 mounted on and communicating with a closed trough or conduit 23. 1 The conduit 23 extends alongthe entiresideofthefiumaceandismountedata slight inclination towards a molten metal sump or collecting pot 24 of relatively large capacity arranged at one end ofthe furnace structure. Since the conduit 23 slopes downward across the front of the furnace, the downcomers 22.are progressively longer from the end of the furnace remote fromthe collecting pot to the end, adjacent the collecting pot. Each a clean-out opening immediately above the conduit cover 38 normally closed by a brick or the like. The downcomers 22 communicate with r the conduit 23 through apertures 39 .in the conduit cover 38. Each aperture may be closed by inserting a slide damper in place 01'- the brick 25 to prevent the escape of zinc vapor from'the conduit when cleaning or changing retorts or reflux columns. The elbow pipe 21, the downcomer 22 and the conduit 23 may be made of silicon carbide or the like. The conduit 23 is supported by a sheet metal trough 27 lined internally with appropriate refractory material, such for Sufflcient heat radiation is provided for condensing all of the zinc vapor entering the conduit to molten metal. The trough 27, as well as the v reflux columns, are supported by. a suitable framework or brackets 37 secured to the buckstays of the furnace.

The collecting pot is provided with heating means,such as a burner 28 for fuel gas (e. g. carbon monoxide). The heating gases from the burner 28 pass over the surface of the purified zinc metal in the collecting pot' and escape through a stack 29, thus maintaining the zinc.

metal in a uniform molten condition. Each of the two conduits 23 (on opposite sides of the furnace structure) delivers molten metal to a well 30 at one side of the collectingpot 2-1. The wells 30 are separated from the collecting pot 24. by partition walls 30' extending from the roof to a point below the level of molten metal therein. The wells 30 thus communicate with the collecting pot 24 through the channels underneath the partition walls 30' and the wells are thereby sealed to prevent products of combustion .in the collecting-pot entering the condensing system. Above the well 30 a tube'31 extends vertically upward from the conduit 23. The vertical tube 31 is of such height and is'soconstructed as to insure substantially complete condensation to molten zinc of such residual zinc vapor as may find its way into the tube. Thecollecting pot 24 has a dipping well 32 fr m which molten metal lrinkay be removed as de ed for casting and the Each retort 13 is provided with a charging well 33 communicating with the retort through n elbow pipe 34. Molten zinc metal to be purified is poured from a char ing ladle 35 into a trough 36 dischar ing into the well 33.

Inpracticing the invention in the apparatus illustrated in the drawings, the vapor evolved from the baths of boiling zinc metal in the retorts l3passes through the elbows'14 into the associated reflux columns. The zinc, vapor is purified with respect ,to lead by refluxing and/0r rectification in the reflux or rectifying columns 10. The resulting purified zinc vapor passes out of the reflux columns, through the elbow pipes 21, and is condensed to molten zinc in the downcomers 22 and the conduit 23. The purified molten zinc flows down the conduit, on either side of the furnace, into the wells 30 and thence to the collecting pot 24, from which it is ladled out as desired from the dipping well 32.

downcomer 22 hasexample as tamped loam or clay 26.

Molten zinc metal (of the grade to be refined) .is charged from time to time (or continuously if desired) into each operating retort (through the troughs 38 and wells 33) to maintain an approximately uniform volume of molten metal in each retort. A certain proportion (say around 10 to 30%) of the zinc vapor enteringeach reflux column is ultimately returned to its associated retort as molten metal in consequence of the refluxing action. This refluxed molten metal contains the lead moved from the zinc vapor, and its return .to the retort results in progress sively increasing the lead content of the molten metal therein. Each retort is continuously operated until the lead content of the molten metal therein has progressively increased to such a high percentage that the vapor delivered by its associated reflux column to the condensing system has as high a lead content as can be tolerated in the condensing system. Such a retort is then cutout of operation, is cleaned of the lead-high metal therein, and is then recharged with molten zinc metal of the grade undergoing purification. Starting with the initial char ing .of a retort with zinc metal of the grade to be purified, the lead content of the molten metal in the retort gradually increases in consequence of distillation and the refluxing action, and consequently the lead content of the purified zinc vapor delivered to the condensing -system from this retort correspondingly increases. In other words, zinc vapor of the highest purity is' delivered to the condensing system from an initially or freshly charged retort and the purity of the zinc vapor delivered to the condensing system progressively decreases .as the retort continues in operation with periodic charging but without cleaning. In accordance with the invention, a continuously uniform purified zinc metal is obtained bycombining or blending the zinc vapor from a plurality of retorts in diflerent stages of the working-off period between a freshly or initially charged retort and the cleaning out of the retort when the'lead content of the molten metal therein attains a predetermined maximum value. In practice, this result is brnught about by cleaning out and freshly charging the retorts in sequence over the working-off period. Thus, with a furnace of-24 recharged each day. In consequence of this method of cleaning out and charging the retorts in sequence, the total amount of lead present in the system of volatilizing retorts is kept substantially constant, and therefore the degree of .purity of the redistilled zinc produced likewise tends to remain constant. Furthermore, the delivery of the blended condensed metal (from the reflux columns of a plurality of distillation retorts containing molten metal of progressively varying lead content) to a relatively large pool of molten metal tends. further to a uniforming of the purified product ladled or otherwise with- 4 drawn from the collecting pot 24.

' The following specific example of the practice of the invention is illustrative d in no sense restrictive or limiting of its scope or application. The 'fumace contains twenty-eight re-' torts, fourteen on each side,-of the spelter retort type, approximately 5 feet long and 7-10 inches internal diameter (oval section). The fire clay cylinder 15 of the reflux column is 2 ft. 3 in. high and 7 in. internal diameter, with a wall thickness of l in. The steel casing 18 is 12 7 in diameter and the annular space :between the tort, of which approximately was condensed in the reflux column and returned to the retort as molten metal. The furnace as a whole thus produced about 26.9 tons of purified zinc metal per day, which was withdrawn from the dipping well 32. The retorts were charged at minute intervals with -35 pounds per retort of molten metal of the grade. undergoing purification to maintain a substantially constant volume of molten metal in each retort. Five to six retorts in the furnace were cleaned out .and freshly charged each'day, so that the continuous working eriod or cycle of each retort in the furnace was about 5 days. The molten metal withdrawn from the retort in cleaning out contained aw proximately 4 lead. The purified zinc metal withdrawn from the collecting and uniforming pct 24 contained 003% lead. The lead content of the zinc vapor delivered tothe condensing system by a freshly charged retort was approximately .001%, and by a retort immediately preceding its cleaning out approximately .006%.'

The remainingretorts delivered to the condensing system zinc vapor of progressively. varying intermediate lead content depending upon their respective stages or relative positions in the working cycle .of continuous retort operation. From 15-18-tons of purified molten metal were main-. tained in the collecting pot 2%;

The construction of reflux column illustrated in Figs. 1, 2 and 31s simple, inexpensive and gives -very satisfactory results in practice. Various modifications may be made in the construction of the reflux column. 'Insuch a modification illustrated in Fig. 4, the reflux column consists of a stack of pots or trays 40 of fire clay, silicon'carhide or equivalent refractory material. The pots 40 are rectangular inform with side walls 41 beveled in such fashion that the pots can be stacked one above the other.' The bottom of each pot has a transverse slot or opening 42 approximate one end thereof. The :upper surface of the bottom of each pot is provided with transverse ribs 43, parallel to the slot 42; the ribs being of progressively increasing height from the end nearest the slot to the end furthest from the slot. The pots 40 are stacked in staggered relationship so that the bottoms thereof form a column of superposed horizontal battles through which metallic vapor ascends and molten metal descends in zig-zag paths. The ribs 43 serve to retain shallow pools of molten metal on the bot toms ofthe pots, The cascade eifect of molten metal'pouring over the ribs'facilitates intimate contact between the ascending vapor and the descending molten metal. The top of the reflux column is closed by a plate or cover 44 through which extends an off-take pipe 45 leading to the downcomer 22 of the condensing system. The assembly of stacked pots 40'is heat insulated in any appropriate manner, as for example by refuse zinc oxide 1'? confined in place by a steel casing 18. With a reflux column generally of.

this type, there was obtained, in'a run of seven.

days continuous operation, a purified zinc metal product containing less than 0.002% lead, from a high lead zinc containing up to 1.0% lead. The

, The invention may lie-carried out in various forms and types of apparatus other than that illustrated in the accompanying drawings. The I fore described. Othertypes of retorts maybe used for volatilizing the impure zinc to be refined. Thus, the impure metal may be volatilized in a crucible equipped with internal electric resistors; or an externally heated built-up retort may be used instead of the specific type of retort hereinbefore described.

This application is a division of my application Serial No. 648,056, filedDecember 20, 1932.

. rc a 1-. Themethod of purifying zinc by redistillation which comprises zinc contaminated with lead in a continuously operated system containing a number of separate retorts. adding impure zinc of the grade to be purified to said retorts asrequired to maintain a substantally uniform volume of molten metal in each retort,

. maintaining the total amount of lead present in said system of distillation retorts substantially constant by withdrawing the retorts from continuous operation in periodic sequence forthe removal therefrom of metal of relatively high lead content and the recharging thereof with impure zinc of the grade tobe purified, passing the vapor from each retort through a reflux column operatlvely'associated therewith, and conducting the purified zinc vapor from each ofsaid reflux columns to a common condensing and collecting 2. The method of purifying zinc. by redistilla tion which comprises distilling zinc contaminated with lead in a continuously operated system containing anumber ofseparate retorts, adding impure zinc of the grade to be purified to said retorts as required to maintain a sub ntially uniform volume of molten metal in eac retort, withdrawing lead-rich residues from the individual retorts at different times without interrupting the lead present in the distillation retorts remains substantially constant, passing the vapor from each retort through a reflux column operatively continuity of operation of the sys- V tem and in such a way that the total amount of ciated therewith,'and conducting the purified zinc vapor from each of said reflux columns to a' common condensing system. a

4. The method of purifying zinc which comprises distilling zinc in a plurality of retorts containing zinc metal of progressively varying lead content in consequence of the continuous operation of said retorts for progressively difierent lengths of time, passing the vapor from each re- Y tort through a reflux column operatively associatedtherewith, and conveying the purified zinc vapor from each of said reflux columns through a common condensing system to arelatively of the grade to be purified and large accumulated bath of purified molten metal.

substantially uniform volume of molten metal in' each retort by the addition'thereto of zinc of the grade to be purified, and cleaning out and freshly charging the retorts in periodic sequence through the working cycle of continuous-retort operation.

6. The method of prises distilling zinc in a plurality of retorts containing zinc metal of progressively varying lead content in consequence of the continuous operation of said retorts for progressively differentv lengths of time, adding zinc metal to said retorts as required to maintain a substantially uniform volume oi. molten metal in each retort, passing the vapor from each retort through a reflux column operatively associated therewith, col ecting, in a common reservoir the molten meta resulting from the purified vapor delivered by each reflux columns, and withdrawing said retorts in periodic sequence from continuous operation as aforesaid for the removal therefrom of metal of relatively high lead content and the freshly charging thereof with impure zinc metal.

'7. The method of tionw with lead ina continuously operated system contai g vapor from each retort through a reflux column operatively associated therewith, conducting the Purified zinc vapor from each of said reflux colntent, passing purifying zinc which com- I p rifying zinc by redistilla-. ch comprises distilling zinc contaminated a number ofseparate'retorts, passing the" umns to a common condensing and collecting system, adding impure zinc of the grade to be purifled to' said retorts as required to maintain a substantially uniform volume of molten metal in each retort, and withdrawing lead-rich residues from the individual retorts at diiferent times without interrupting'the continuity of operation of the system and in such'a way that the total amount of lead present in the distillation retorts remains'substantially constant whereby the degree of purity of the refined zinc product likewise tends to remain constant. k

8.. The method of purifyingzinc by redistillation which comprises introducing impure unvaporized zinc into a plurality of separate retorts through the end portions thereof, vaporizing the zinc in'said retorts, withdrawing the resulting zinc vapor from the same ends of the retorts through which the unvaporized zinc is introduced, subjecting the vapor from each retort to a separate reflux condensation treatment, and conducting the purified zinc vapor from each of said separate reflux condensation treatments to a comm"on condensing and cooling system.

9. The method of purifying zinc byredistillation which comprises introducing impure unvaporized zinc into a plurality of separate retorts through the end portions thereof, vaporizing the Y zinc in said retorts, withdrawing the resulting zinc vapor from the same ends of the retorts through which the unvaporized zinc is introduced, subjecting the vapor from each retort to a separate reflux condensation treatment,.con-

ductingthe purified zinc vapor from each of said separate reflux condensation treatments through reservoir of accumulated pin-med molten metal,

- nd'supplying' extraneous heat to said reservoir to maintain the purified metal in molten form.

I PHJIJP Ml onmnn.

s a common condensing ystem to a relatively large g 

